CN112558065B - A three-dimensional imaging method based on a reconfigurable electromagnetic surface array - Google Patents

Abstract

According to the three-dimensional imaging method of the reconfigurable electromagnetic surface array of the present disclosure, the reconfigurable electromagnetic surface array is constructed according to the target area, the N transmitting sub-arrays and the N receiving sub-arrays are corresponding and orthogonal, and the adjacent sub-array elements partially overlap, N is a positive integer; the multi-channel transmitting digital beam and its corresponding multi-channel receiving digital beam are orthogonal to the multi-channel digital composite beam of the transceiver sub-array, and focus on the corresponding position of the target area as the transceiver sub-array scanning beam; The phase compensation of the overlapping array elements of the array and the receiving sub-array enables the multi-channel digital composite beam to focus on different positions in the target area; the target area is divided into multiple parallel sections, and the transceiver sub-array scanning beam and multiple parallel sections are combined on each parallel section. The three-dimensional imaging of the target area is obtained by scanning the channel digital composite beam. It can reduce the number of spatial scans by several orders of magnitude, integrate the advantages of sparse array and real beam imaging, and realize fast pass-through security inspection when there is a large flow of people, and quickly scan and image the human body.

Description

A three-dimensional imaging method based on a reconfigurable electromagnetic surface array

technical field

The invention belongs to the technical field of security inspection, and in particular relates to a three-dimensional imaging method based on a reconfigurable electromagnetic surface array.

Background technique

The issue of public safety is the focus of widespread concern of the international community. Airports, subways, stations, squares and other densely populated places are the main locations for attacks, so higher requirements are also placed on the accuracy, real-time, intelligence and environmental applicability of the security inspection system.

In recent years, millimeter wave security inspection imaging technology is a new type of security inspection technology. It has the advantages of high safety, good penetration, and different electromagnetic scattering characteristics of different materials. It has become the mainstream development direction of human security inspection technology.

Millimeter wave security inspection imaging is mainly divided into two modes: active and passive. The active imaging method is less dependent on the environment, the amount of information obtained is more abundant, and the image signal-to-noise ratio and contrast are high. The three-dimensional imaging of the target can be achieved mainly by the millimeter-wave single-channel two-dimensional mechanical scanning imaging system developed by the JPL laboratory in the United States. ; The ProVision millimeter-wave body imaging security inspection system developed by L3 Company in the United States combines electrical scanning and mechanical scanning; the QPS millimeter-wave imaging system based on MIMO area arrays by Rohde & Schwarz in Germany, and the Eqo imaging system based on two-dimensional reflectors by Smith Detection in the United Kingdom. While the United Kingdom and the United States and other countries carry out research on human security imaging technology in the terahertz frequency band, most of them use passive systems.

Reconfigurable digital electromagnetic surfaces have attracted extensive attention and research. Integrate semiconductor electronic devices or micro-electromechanical systems (MEMS) in the design of reconfigurable digital electromagnetic surface units, so that the array radiation and phase modulation devices are combined into one, and the reconfigurable antenna has the advantages of traditional reflector antennas and phased array antennas , thin and easy to conform, easy to form a large surface, easy to develop to high frequency, and the millimeter wave band can use a relatively mature semiconductor process to achieve high-precision, low-cost mass production.

The reconfigurable electromagnetic surface uses the voltage-controlled diode to control the reflection unit, and the beam space scanning can be realized without multiple radio frequency channels. The reconfigurable electromagnetic surface voltage-controlled diode can replace the traditional antenna array element for the sub-array design of the transceiver array. On the basis of wide beam scanning of electromagnetic surface sub-array, combined with digital beam scanning, three-dimensional high-resolution imaging can be completed, which improves beam scanning efficiency.

Digital Beamforming (DBF) technology is widely used in ultrasonic, radar signal processing and electronic countermeasure systems. It uses the weighted summation of the signals received by the array antenna from different directions in space to form a specific pointing digital signal. The beam, the weight vector of the weighted summation determines the beam pointing, null and side lobe levels, and realizes beam scanning, target tracking, and null for spatial interference signals. In such applications, the signal model is usually based on the far-field plane wave, while in the near-field millimeter-wave human body security imaging, the electromagnetic waves transmitted and received by the antenna are in the form of spherical waves, so the far-field DBF algorithm cannot be directly applied.

In the field of near-field ultrasound fast imaging, the main beamforming algorithms are the near-field dynamic focusing beamforming algorithm based on FFT, the Chirp-z transform algorithm, and the non-uniform fast Fourier transform (NUFFT)-based beamforming algorithm, etc. Several categories.

However, in terms of processing algorithms and system costs, it is difficult for the existing millimeter-wave imaging technologies to meet the requirements of fast-passing human security inspection in densely populated areas at the same time. Therefore, there is an urgent need to explore a new imaging system and method to meet the needs of fast-passing human security inspection in densely populated areas.

SUMMARY OF THE INVENTION

In view of this, the present disclosure proposes a three-dimensional imaging method based on a reconfigurable electromagnetic surface array, which can reduce the number of spatial scans by several orders of magnitude, integrate the advantages of sparse arrays and real-beam imaging, and can realize the passage of people when there is a large flow of people. Type rapid security inspection, rapid scanning and imaging of the human body.

According to an aspect of the present invention, a three-dimensional imaging method based on a reconfigurable electromagnetic surface array is proposed, the method comprising:

A reconfigurable electromagnetic surface array is constructed according to the three-dimensional imaging target area, the reconfigurable electromagnetic surface array includes N reconfigurable electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, the N reconfigurable electromagnetic surface receiving sub-arrays Constructed electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, and adjacent reconfigurable electromagnetic surface emitting sub-arrays or adjacent reconfigurable electromagnetic surface receiving sub-arrays Some of the array elements overlap, and N is a positive integer;

For each reconfigurable electromagnetic surface emitting sub-array, the multi-channel transmitting digital beam and the corresponding multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving sub-array are spatially orthogonal, and are combined into a multi-channel receiving and transmitting sub-array. The digital composite beam, which is focused on the corresponding position of the 3D imaging target area, is the transmitting and receiving sub-array scanning beam;

Phase compensation is performed on the overlapping array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, and the phase and The reconfigurable electromagnetic surface receives the phase of the multi-channel received digital beams of the sub-arrays, so that the multi-channel digital composite beams of different transceiver sub-arrays are focused to different positions in the three-dimensional imaging target area, and multiple transceiver sub-array scanning beams are obtained ;

The three-dimensional imaging target area is divided into a plurality of parallel sections, and on each parallel section, the wide beam scanning of the scanning beam of the transceiver sub-array and the multi-channel digital synthesis beam are combined in the main lobe of the transceiver sub-array The 3D imaging of the 3D imaging target area is obtained by scanning the narrow beam.

In a possible implementation, the reconfigurable electromagnetic surface emitting sub-array includes a transmitting feed, a diode phase control array and an antenna unit;

The reconfigurable electromagnetic surface receiving sub-array includes a receiving feed, a diode phase control array and an antenna element.

In a possible implementation manner, the adjusting the phase of the multi-channel transmit digital beam of the reconfigurable electromagnetic surface emitting sub-array and the phase of the multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving sub-array, include:

By adjusting the on-off state of the diode phase control array of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, the phase of the antenna elements of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array is adjusted, according to The antenna elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array phase adjust the phase of the multi-channel transmitting digital beam and the phase of the multi-channel receiving digital beam to form a transceiving sub-array scanning beam.

In a possible implementation manner, digital beam synthesis is performed on the multi-channel transmit signal according to adjusting the phase of the transmit feed signal, and digital beam synthesis is performed on the multi-channel transmit signal according to the phase adjustment of the transmit feed. The beamforming is spatially orthogonal to the multi-channel digitally synthesized beams of the transceiver sub-arrays.

In a possible implementation manner, performing phase compensation on the overlapping array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array includes:

According to the phase distribution of the overlapping part of the array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, the matching adjustment method of the average phase is used for the reconfigurable electromagnetic surface emitting sub-array or the reconfigurable electromagnetic surface-emitting sub-array. Phase compensation is performed on the overlapping part of the array elements of the reconstructed electromagnetic surface receiving sub-array.

In a possible implementation, a non-uniform fast Fourier transform algorithm is used to obtain the multi-channel transmitting digital beam of the reconfigurable electromagnetic surface emitting sub-array and the corresponding multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving sub-array The beams are spatially orthogonal to the multi-channel digital composite beams of the transceiver sub-arrays.

In a possible implementation manner, the total array of reconfigurable electromagnetic surfaces is a cross shape, a T shape, or a Γ shape.

In the three-dimensional imaging method based on the reconfigurable electromagnetic surface array of the present disclosure, a reconfigurable electromagnetic surface array is constructed according to the three-dimensional imaging target area, and the reconfigurable electromagnetic surface array includes N reconfigurable electromagnetic surface emission sub-arrays and N Reconfigurable electromagnetic surface receiving sub-arrays, the N reconfigurable electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are spatially orthogonal, and adjacent reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence. Part of the array elements of the surface-emitting sub-array or adjacent reconfigurable electromagnetic surface-receiving sub-arrays overlap, and N is a positive integer; for each reconfigurable electromagnetic surface-emitting sub-array, the multi-channel transmitting digital beam and its corresponding reconfigurable electromagnetic surface-emitting sub-array The multi-channel receiving digital beam of the electromagnetic surface receiving sub-array is orthogonal in space to the multi-channel digital composite beam of the transceiver sub-array, and the corresponding position focused on the three-dimensional imaging target area is the transceiver sub-array scanning beam; Phase compensation is performed on the overlapping elements of the electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array to adjust the phase of the multi-channel transmitted digital beam of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface emitting sub-array. The multi-channel receiving sub-arrays of the surface receive the phase of the digital beam, so that the multi-channel digital composite beams of different transceiver sub-arrays are focused to different positions in the three-dimensional imaging target area to obtain a plurality of transmitting and receiving sub-array scanning beams; the three-dimensional imaging The target area is divided into a plurality of parallel sections, and each parallel section is obtained by combining the wide beam scanning of the scanning beam of the transceiver sub-array and the narrow beam scanning of the multi-channel digital composite beam in the main lobe of the transceiver sub-array Three-dimensional imaging of the three-dimensional imaging target area. It can reduce the number of spatial scans by several orders of magnitude, integrate the advantages of sparse array and real beam imaging, and realize fast pass-through security inspection when there is a large flow of people, and quickly scan and image the human body.

Other features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.

1 shows a flowchart of a three-dimensional imaging method based on a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;

2a and 2b respectively illustrate schematic diagrams of a reconfigurable electromagnetic surface array security inspection according to an embodiment of the present disclosure;

FIG. 3 shows a schematic diagram of a cross-shaped reconfigurable electromagnetic surface array topology according to an embodiment of the present disclosure;

4a-4d illustrate schematic diagrams of overlapping multiplexing of sub-arrays of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;

FIG. 5 shows a schematic diagram of a reconfigurable electromagnetic surface array scanning according to an embodiment of the present disclosure;

FIG. 6a shows a schematic diagram of composite beamforming in which the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array are not multiplexed according to an embodiment of the present disclosure;

FIG. 6b shows a schematic diagram of a composite beam scanning result multiplexed by a reconfigurable electromagnetic surface emitting sub-array and a receiving sub-array according to an embodiment of the present disclosure;

6c shows a schematic diagram of a composite beam scanning result without multiplexing of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array according to an embodiment of the present disclosure;

FIG. 6d shows a composite beam scanning beam comparison diagram before and after multiplexing of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array according to an embodiment of the present disclosure;

7 shows a schematic diagram of multiplexing and matching of a reconfigurable electromagnetic surface emitting sub-array and a receiving sub-array according to an embodiment of the present disclosure;

Figure 8a shows a cross-section of an azimuth view of a reconfigurable electromagnetic surface emitting sub-array and a receiving sub-array multiplexing according to an embodiment of the present disclosure;

Fig. 8b shows a cross section of an azimuth view of a reconfigurable electromagnetic surface emitting sub-array and a receiving sub-array that are not multiplexed according to an embodiment of the present disclosure;

9 shows a schematic diagram of a near-field digital composite beam of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;

FIG. 10 shows a schematic diagram of near-field focusing dynamic depth of field of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;

FIG. 11 shows a schematic diagram of a near-field focusing dynamic depth of field simulation result of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure.

Detailed ways

Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numbers in the figures denote elements that have the same or similar functions. While various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following detailed description. It will be understood by those skilled in the art that the present disclosure may be practiced without certain specific details. In some instances, methods, means, components and circuits well known to those skilled in the art have not been described in detail so as not to obscure the subject matter of the present disclosure.

FIG. 1 shows a flowchart of a three-dimensional imaging method based on a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure. As shown in Figure 1, the method may include:

Step S11 : constructing a reconfigurable electromagnetic surface array according to the three-dimensional imaging target area, the reconfigurable electromagnetic surface array includes N reconfigurable electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, the N Reconfigurable electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are spatially orthogonal, and adjacent reconfigurable electromagnetic surface emitting sub-arrays or adjacent reconfigurable electromagnetic surface Part of the array elements of the receiving subarray overlap, and N is a positive integer.

The reconfigurable electromagnetic surface transmitting array and the reconfigurable electromagnetic surface receiving array are orthogonal in space, that is, the N reconfigurable electromagnetic surface transmitting arrays and the N reconfigurable electromagnetic surface receiving arrays are also orthogonal in space, and can be The multi-channel transmitting digital beams of the reconfigurable electromagnetic surface emitting sub-array and the multi-channel receiving digital beams of the corresponding reconfigurable electromagnetic surface receiving sub-array are also orthogonal in space.

2a and 2b respectively illustrate schematic diagrams of a reconfigurable electromagnetic surface array security inspection according to an embodiment of the present disclosure. FIG. 3 is a schematic diagram illustrating the topology of a cross-shaped reconfigurable electromagnetic surface array according to an embodiment of the present disclosure.

As shown in Figures 2a and 2b, the scale of the human imaging area is 0.4m (range direction), 0.8m (azimuth direction), and 2.0m (height direction). According to the scale of the three-dimensional human imaging area, a reconfigurable electromagnetic surface array ( The cross-shaped reconfigurable electromagnetic surface array in Figure 2). Different cross-shaped reconfigurable electromagnetic surface arrays in Figs. 2a and 2b are respectively responsible for imaging corresponding human target regions. Among them, the horizontal square represents the reconfigurable electromagnetic surface emitting sub-array, and the vertical square represents the reconfigurable electromagnetic surface receiving sub-array. Reconstruct the total array of electromagnetic surface transceivers. Different cross modules in Figures 2a and 2b respectively image the corresponding human target regions.

As shown in Figure 3, the upper plane is the focal plane, and R ₀ is the distance between the reconfigurable electromagnetic surface and the focal plane. The x-direction (the transverse squares of the cross-shaped reconfigurable electromagnetic surface array in Figures 2a and 2b) is the emission array of the cross-shaped reconfigurable electromagnetic surface array, that is, the N transverse square arrays represent the cross-shaped reconfigurable electromagnetic surface emitters The y-direction (the vertical squares of the cross-shaped reconfigurable electromagnetic surface array in Figures 2a and 2b) is the receiving array of the cross-shaped reconfigurable electromagnetic surface array, that is, the N vertical square arrays represent the cross-shaped reconfigurable electromagnetic surface array. Electromagnetic surface receiving subarray. The transmitting array of the cross-shaped reconfigurable electromagnetic surface array and the receiving array of the cross-shaped reconfigurable electromagnetic surface array together constitute a total cross-shaped reconfigurable electromagnetic surface transmitting and receiving array, and N reconfigurable electromagnetic surface transmitting sub-arrays and N There is a one-to-one correspondence between the reconfigurable electromagnetic surface receiving subarrays, and N is a positive integer. Of course, the horizontal square of the cross-shaped reconfigurable electromagnetic surface array is the receiving array of the cross-shaped reconfigurable electromagnetic surface array, that is, the N horizontal square arrays represent the cross-shaped reconfigurable electromagnetic surface receiving sub-array; the vertical square is a cross-shaped reconfigurable electromagnetic surface array. The emission array of the reconfigurable electromagnetic surface array, that is, a vertical square array represents a cross-shaped reconfigurable electromagnetic surface emission sub-array, which is not limited here. In addition, the spatial structures of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array can also be T-shaped, Γ-shaped, etc., which are not limited here, as long as the transmitting array of the reconfigurable electromagnetic surface array and the reconfigurable electromagnetic surface array It is sufficient that the receiving arrays of the surface array are spatially orthogonal. When each cross-shaped reconfigurable electromagnetic surface transceiving total array works, all the reconfigurable electromagnetic surface transmitting sub-arrays and receiving sub-arrays work simultaneously, and the phased array mode is used to achieve real-time high-resolution imaging of the target area.

In an example, as shown in FIG. 3, the N reconfigurable electromagnetic surface emitting sub-arrays may include transmit feeds, diode phase control arrays and antenna elements; the N reconfigurable electromagnetic surface receiving sub-arrays may include receiving feeds , diode phase control unit and antenna unit. The phase of the array elements of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array can be adjusted by controlling the on-off state of the voltage-controlled diode.

4a-4d illustrate schematic diagrams of overlapping multiplexing of sub-arrays of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure.

The sub-array can be either a reconfigurable electromagnetic surface-emitting sub-array or a reconfigurable electromagnetic surface-receiving sub-array. Taking the reconfigurable electromagnetic surface receiving array as an example to illustrate, as shown in Figures 4a-4d, the reconfigurable electromagnetic surface receiving array may include 4 receiving feeds, from left to right are the first receiving feed, the second receiving feed A receiving feed, a third receiving feed, and a fourth receiving feed. As shown in Figure 4a, the first receiving feed corresponds to the first 6*6 antenna unit and its diode phase control array (the first reconfigurable electromagnetic surface receiving sub-array). As shown in Figure 4b, the second receiving feed The source corresponds to the second 6*6 antenna element and its diode phase control array (the second reconfigurable electromagnetic surface receiving sub-array), the first sub-array and the second sub-array are overlapped and multiplexed from left to right 4-6 A column of 3*6 antenna elements and their diode phase control array, as shown in Figure 4c, the third receiving feed corresponds to the third 6*6 antenna element and its diode phase control array (the third reconfigurable Electromagnetic surface receiving subarray), the second subarray and the third subarray overlap and multiplex the 3*6 antenna elements and their diode phase control arrays in the 7th to 9th columns from left to right, as shown in Figure 4d, the fourth The receiving feed corresponds to the fourth 6*6 antenna unit and its diode phase control array (the fourth reconfigurable electromagnetic surface receiving sub-array), the third sub-array and the fourth sub-array are overlapped and multiplexed from left to right 10th -12 columns of 3*6 antenna elements and their diode phase control arrays.

Step S12: The multi-channel transmit digital beams of each reconfigurable electromagnetic surface emitting sub-array and the corresponding multi-channel receiving digital beams of the reconfigurable electromagnetic surface receiving sub-array are spatially orthogonal to the multi-channel transmitting and receiving sub-arrays The digital composite beam is focused on the corresponding position of the 3D imaging target area as the transmitting and receiving sub-array scanning beam.

In an example, the on-off state of the array can be controlled by adjusting the diode phase of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array, and the phase of the antenna elements of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array can be adjusted. The antenna elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array phase adjust the phase of the multi-channel transmitting digital beam and the phase of the multi-channel receiving digital beam to form a transceiving sub-array scanning beam.

In an example, digital beamforming can be performed on the multi-channel transmit signal according to the phase adjustment of the transmit feed signal, and the digital beamforming of the multi-channel transmit signal by adjusting the phase of the transmit feed is spatially orthogonal to a transceiver sub-array. multi-channel digital synthesis beam.

FIG. 5 shows a schematic diagram of a reconfigurable electromagnetic surface array scanning according to an embodiment of the present disclosure.

As shown in Fig. 3, for each antenna element with a 16*16 reconfigurable electromagnetic surface emitting sub-array and its diode phase control, the transmitting feed of the reconfigurable electromagnetic surface emitting sub-array illuminates the antenna element, and the diode phase is adjusted by adjusting the antenna element. The control array controls the phase of the antenna unit, so that the multi-channel transmit digital beam of the transmit sub-array is focused on a certain part of the imaging area; by adjusting the phase of the transmit feed signal, digital beam synthesis is performed on the multi-channel transmit digital beam signal, as shown in Figure 5. The multi-channel transmit digitally scanned beam. The 16*16 antenna elements of the reconfigurable electromagnetic surface receiving sub-array corresponding to the 16*16 reconfigurable electromagnetic surface emitting sub-array are controlled by the diode phase control array corresponding to each element to make the receiving sub-array The multi-channel receiving digital beam is focused on the same area where the transmitting array is focused; by adjusting the phase of the receiving feed signal, digital beam synthesis is performed on the multi-channel receiving signal, and the multi-channel receiving digital beam (receiving digital scanning beam) reflected from the target area is received. shown in Figure 5. The multi-channel transmitting digital scanning beam and the multi-channel receiving digital scanning beam are spatially orthogonal to the multi-channel digital composite beam of the transceiver sub-array (transmitting and receiving composite beam in Figure 5), as shown in the black dot in the center of the plane as shown in Figure 5.

The ideal cos ^q (θ) model is used for the feed and radiation pattern of the reconfigurable electromagnetic surface array. Taking the (m,n) unit as an example, the amplitude of the transceiving synthetic beam at the black point of the focal plane is:

其中，

为可重构电磁表面阵列单元路径相位，

为可重构电磁表面阵列单元可调相位。若要在聚焦点处实现所有阵列单元等相位叠加，可重构电磁表面阵列单元的相位特性需要满足：

in,

is the reconfigurable electromagnetic surface array element path phase,

Adjustable phase for reconfigurable electromagnetic surface array elements. To achieve equal phase superposition of all array elements at the focal point, the phase characteristics of the reconfigurable electromagnetic surface array elements need to satisfy:

由于可重构电磁表面阵列单元具有离散的相位特性，可以采用可重构电磁表面阵列单元的相位状态的最大值进行判定：

依据此方法，遍历发射子阵和接收子阵的所有阵元，可以使所有发射子阵波束和接收子阵波束在空间上正交且聚焦于目标平面的相应位置。

Since the reconfigurable electromagnetic surface array unit has discrete phase characteristics, the maximum value of the phase state of the reconfigurable electromagnetic surface array unit can be used to determine:

According to this method, by traversing all the array elements of the transmitting sub-array and the receiving sub-array, all the beams of the transmitting sub-array and the receiving sub-array can be made spatially orthogonal and focused on the corresponding position of the target plane.

Step S13: Perform phase compensation on the overlapping array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, and adjust the multi-channel transmitting digital beam of the reconfigurable electromagnetic surface emitting sub-array and the phase of the multi-channel digital beam received by the reconfigurable electromagnetic surface receiving sub-array, so that the multi-channel digital composite beams of different transceiver sub-arrays are focused to different positions in the three-dimensional imaging target area, and multiple transceiver sub-arrays are obtained. Array scanning beam.

The traditional phased array constitutes the above-mentioned cross transceiver array, which can also achieve scanning imaging of the target area. However, due to the large scanning range, the array element spacing is small (half wavelength is optimal), resulting in a large number of RF channels. Considering the cost and scanning efficiency of the 3D imaging system, the composite beam scanning system is adopted, and the beam scanning can be realized by controlling the phase of the diode control unit of the reconfigurable digital electromagnetic surface by using the undersampling design, and the cost is low. Through the reconfigurable electromagnetic surface emitting sub-array and receiving sub-array, the target imaging area is subjected to wide-beam scanning of the sub-array scanning beam, and the DBF (transmit-receive composite beam) fine scanning is used in the main lobe range of the transceiver sub-array, which can achieve high Resolution 3D near-field imaging.

Taking the reconfigurable electromagnetic surface receiving array as an example, according to the pattern product theorem, the total array pattern can be expressed as the multiplication factor of the reconfigurable electromagnetic surface receiving subarray element (SA Subarray Pattern) and the reconfigurable electromagnetic surface receiving subarray. The form of the product of the channel array factor (SA Backend AF Pattern), as shown in Figure 6a, can effectively suppress the grating lobe of the DBF. When the reconfigurable electromagnetic surface-emitting sub-array and the reconfigurable electromagnetic surface-receiving sub-array are arranged side by side, the equivalent array element spacing is the array length of the reconfigurable electromagnetic surface-emitting sub-array or the reconfigurable electromagnetic surface-receiving sub-array , when the DBF scans, the grating lobe will enter the two adjacent zero points of the main lobe of the reconfigurable electromagnetic surface emitting sub-array or the reconfigurable electromagnetic surface receiving sub-array, but will not enter the 3 dB main lobe. In order to increase the scanning margin of the reconfigurable electromagnetic surface emitting sub-array or the reconfigurable electromagnetic surface receiving sub-array, the overlapping multiplexing undersampling of the reconfigurable electromagnetic surface emitting sub-array and the receiving sub-array as shown in Fig. 4a-4d is adopted. It is designed so that the DBF grating lobe is always outside the zero point of the main lobe, which further reduces the interference of surrounding targets.

Using the digital beamforming method in which the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array are partially overlapped (the reconfigurable electromagnetic surface emitting sub-array or the receiving sub-array overlaps), the multi-channel can be formed. The reconfigurable electromagnetic surface transmitting or receiving subarray factor has a better match with the reconfigurable electromagnetic surface transmitting or receiving subarray pattern, keeping the grating lobes of the DBF always in the direction of the reconfigurable electromagnetic surface transmitting or receiving subarray inside the side lobe of the figure. As shown in Figures 6b and 6c, the reconfigurable electromagnetic surface sub-arrays (transmitting sub-arrays or receiving sub-arrays) are shown in the case of multiplexing of elements of the theoretically reconfigurable electronic surface receiving sub-arrays and transmitting sub-arrays. The relationship between the far-field pattern and the total array factor of the reconfigurable electromagnetic surface (the pattern corresponding to the DBF, and there is a certain scanning angle). Figure 6d shows the comparison of the far-field pattern results between the array element multiplexing and non-multiplexing of the theoretically reconfigurable electronic surface receiving sub-array and the transmitting sub-array, which proves that when the electronic surface receiving sub-array and the transmitting sub-array are reconstructed, the When the elements of the sub-array are multiplexed, the DBF grating lobes are significantly suppressed.

For the reconfigurable electromagnetic surface array working in the near field, the scanning mode of digital beam synthesis of the transmit and receive channels is adopted. The reconfigurable electromagnetic surface emission array requires real beam scanning, N reconfigurable electromagnetic surface emission sub-arrays work at the same time, and the phase configuration of two adjacent reconfigurable electromagnetic surface emission sub-arrays is overlapped and multiplexed, as shown in the figure As shown in Fig. 7, for the N array elements of the multiplexing part of two adjacent reconfigurable electromagnetic surface emission sub-arrays, take the i-th (i=1, 2, 3, . It is illustrated that the wave paths generated by the corresponding two reconfigurable electromagnetic surface-emitting sub-array feeds and the phase distribution to be compensated can be expressed as:

分别表示该阵元到相应可重构电磁表面发射子阵馈源的距离，(x_i,y_i)表示该阵元的水平垂直坐标。θ表示该阵元到聚焦位置的俯仰角，

表示该阵元到聚焦位置的方位角。Among them, k ₀ represents the wave number of the corresponding radio frequency,

respectively represent the distance from the array element to the corresponding reconfigurable electromagnetic surface-emitting sub-array feed, and (x _i , y _i ) represent the horizontal and vertical coordinates of the array element. θ represents the pitch angle of the array element to the focus position,

Indicates the azimuth angle from the array element to the focus position.

以此对可重构电磁表面发射子阵或可重构电磁表面接收子阵的重叠部分进行相位补偿。可以补偿可重构电磁表面发射子阵和所述可重构电磁表面接收子阵的重叠阵元进行相位补偿，使不同收发子阵的所述多通道数字合成波束聚焦到三维成像目标区域的不同位置。In an example, according to the phase distribution of the overlapping part of the array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, the matching adjustment method of the average phase is used for the reconfigurable electromagnetic surface emitting sub-array. Phase compensation is performed on the overlapping portion of the array or reconfigurable electromagnetic surface receiving sub-arrays. where the average phase can be

In this way, the phase compensation is performed on the overlapping part of the reconfigurable electromagnetic surface emitting sub-array or the reconfigurable electromagnetic surface receiving sub-array. The overlapping array elements of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array can be compensated for phase compensation, so that the multi-channel digital composite beams of different transceiver sub-arrays can be focused on different areas of the three-dimensional imaging target area. Location.

In an example, by using this method and staggered multiplexing according to the number of 1/2 array elements of the reconfigurable electromagnetic surface sub-array, the reconfigurable electromagnetic surface sub-array reuse coincidence rate is 50%. After discretization, phase compensation is performed, and factors such as illumination range and propagation loss are considered. The obtained near-field digital beam synthesis results at different positions are shown in Figure 8a. Figure 8b shows the result of digital beamforming without multiplexing of the reconfigurable electromagnetic surface sub-array elements. It can be seen from Figures 8a and 8b that the reconfigurable electromagnetic surface sub-array element multiplexing technology combined with the average phase compensation method can maintain the DBF scanning accuracy to a certain extent and effectively reduce the influence of grating lobes.

In an example, in order to further improve the beam pointing accuracy and reduce the side lobe level, the average phase is used as the initial matching, and the particle swarm algorithm is used to optimize the sub-array side lobes. The cost function with low side lobes and low grating lobes as the optimization objective can be expressed by the following formula:

Among them, |F(x _i , y _i )| represents the two-dimensional near-field pattern generated by the ith multiplexed array element, and _ML (x _i , y _i ) represents the expected pattern of the ith array element. The lower envelope, M _U (x _i , y _i ) represents the upper envelope of the pattern that the i-th array element expects to obtain. Compared with the pointing accuracy of the sub-array beam, the impact of low side lobes on the imaging quality is more critical. Since the particle swarm algorithm is more sensitive to the initial value setting, using the matching result of the above average method as the optimized initial phase can improve the iterative process. robustness.

Step S14: Divide the three-dimensional imaging target area into a plurality of parallel sections, and combine the wide beam scanning of the transceiver sub-array scanning beam and the multi-channel digital synthesis beam in the transceiver sub-array on each parallel section. The narrow beam scanning in the main lobe obtains the three-dimensional imaging of the three-dimensional imaging target area.

In an example, the target scene is divided into a plurality of parallel sections, and the dynamic depth of field multi-focusing technology is used to focus each flat section separately, and the wide beam scanning of the transceiver sub-array and the multi-level beam scanning are combined on each parallel section. The near-field three-dimensional imaging of the target area can be obtained by fine scanning (narrow beam scanning) of the channel digital composite beam in the main lobe of the transceiver sub-array. Fig. 10 is a schematic diagram of forming a focused light spot on the target plane when the reconfigurable electromagnetic surface array works in the near-field focusing mode, wherein the reconfigurable electromagnetic surface array is a cross array, and the light spot (subarray scanning beam) is defined as the transceiver subarray The area covered by the 3dB main lobe. The reconfigurable electromagnetic surface array adopts adaptive focus scanning, which can achieve a large depth of field. As shown in Figure 11, the position of the focal-parallel section can be changed in steps of 10cm, and the 3D imaging plane observation spot diameter can be set within the range of ±5cm from the focal plane, so as to achieve a larger distance between the center of the plane and the edge. Dynamic focusing to achieve high-resolution near-field 3D imaging.

In the three-dimensional imaging method based on the reconfigurable electromagnetic surface array of the present disclosure, a reconfigurable electromagnetic surface array is constructed according to the three-dimensional imaging target area, and the reconfigurable electromagnetic surface array includes N reconfigurable electromagnetic surface emission sub-arrays and N Reconfigurable electromagnetic surface receiving sub-arrays, the N reconfigurable electromagnetic surface emitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are spatially orthogonal, and adjacent reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence. Part of the array elements of the surface-emitting sub-array or adjacent reconfigurable electromagnetic surface-receiving sub-arrays overlap, and N is a positive integer; for each reconfigurable electromagnetic surface-emitting sub-array, the multi-channel transmitting digital beam and its corresponding reconfigurable electromagnetic surface-emitting sub-array The multi-channel receiving digital beam of the electromagnetic surface receiving sub-array is orthogonal in space to the multi-channel digital composite beam of the transceiver sub-array, and the corresponding position focused on the three-dimensional imaging target area is the transceiver sub-array scanning beam; Phase compensation is performed on the overlapping elements of the electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface receiving sub-array to adjust the phase of the multi-channel transmitted digital beam of the reconfigurable electromagnetic surface emitting sub-array and the reconfigurable electromagnetic surface emitting sub-array. The multi-channel receiving sub-arrays of the surface receive the phase of the digital beam, so that the multi-channel digital composite beams of different transceiver sub-arrays are focused to different positions in the three-dimensional imaging target area to obtain a plurality of transmitting and receiving sub-array scanning beams; the three-dimensional imaging The target area is divided into a plurality of parallel sections, and each parallel section is obtained by combining the wide beam scanning of the scanning beam of the transceiver sub-array and the narrow beam scanning of the multi-channel digital composite beam in the main lobe of the transceiver sub-array Three-dimensional imaging of the three-dimensional imaging target area. It can reduce the number of spatial scans by several orders of magnitude, integrate the advantages of sparse array and real beam imaging, and realize fast pass-through security inspection when there is a large flow of people, and quickly scan and image the human body.

In a possible implementation, a non-uniform fast Fourier transform algorithm can be used to obtain the multi-channel transmitting digital beam of the reconfigurable electromagnetic surface emitting sub-array and the corresponding multi-channel receiving of the reconfigurable electromagnetic surface receiving sub-array The digital beam is spatially orthogonal to the multi-channel digital composite beam of the transceiver sub-array.

The fast DBF algorithm is usually based on the far-field signal model and cannot be directly applied to near-field imaging; the delay-and-sum algorithm can achieve near-field focusing, but the computational load is too large to be suitable for the fast implementation of the algorithm. The invention proposes a near-field spherical wave wavefront phase compensation method, which performs series expansion approximation on the electromagnetic wave propagation path in the Fresnel area of the antenna array, and uses the matching function to multiply the wavefront phase of the spherical wave. Adopt digital beamforming algorithm to achieve fast dynamic focusing at different distances.

The near-field beamforming algorithm based on non-uniform fast Fourier transform (NUFFT) can be applied to non-uniform sparse array element sampling, laying a foundation for subsequent research on antenna array sparseness, and the computational complexity of the DBF algorithm will be much lower than that of the antenna array. time-accumulation algorithm. Since the beams of the reconfigurable electromagnetic surface transmitting array and the reconfigurable electromagnetic surface receiving array are orthogonal and focused, a one-dimensional beamforming algorithm can be considered. Taking the reconfigurable electromagnetic surface receiving array as an example, the near-field multi-channel digital composite beam algorithm based on NUFFT is introduced.

As shown in FIG. 9 , assuming that the transmitted signal is s(t), the reconfigurable electromagnetic surface emitting linear array has M ₀ antenna units (diode units), wherein each antenna unit is located in a reconfigurable electromagnetic surface sub-array. The one-way signal of the target at (r ₀ , θ) received by the mth antenna unit in the transmitting line array is s(t-τ(r ₀ ,m, θ)), where

对于近场情形，目标成像区域一般位于发射阵列的菲涅尔区(0.96D＜r₀≤D²/2λ)，目标时间延迟可以在最小二乘估计下进行菲涅尔近似：

代入到近场方向图公式中得到：

令θ_start与θ_end为数字合成波束形成的初始角度与结束角度，并等间隔步进N个角度。Let the transmit signal frequency be f, the near-field pattern corresponding to the transmit antenna array can be expressed as:

For the near-field situation, the target imaging area is generally located in the Fresnel region of the transmitting array (0.96D<r ₀ ≤D ² /2λ), and the target time delay can be approximated by Fresnel under the least square estimation:

Substitute into the near-field pattern formula to get:

Let θ _start and θ _end be the initial angle and end angle of digital composite beam forming, and step N angles at equal intervals.

Then any scan angle can be expressed as:

sinθ=pΔs+Δs/2 (N/2≤p≤N/2-1), where

ω_m＝-2πfx_mΔs/c，可以进一步表示为：

由于w'_m(r₀)为非均匀分布，而B(r₀,θ_p)为均匀分布，即可以基于一维NUFFT完成上述近场数字波束形成。make

ω _m =-2πfx _m Δs/c, which can be further expressed as:

Since w' _m (r ₀ ) is a non-uniform distribution, and B(r ₀ , θ _p ) is a uniform distribution, the above-mentioned near-field digital beamforming can be accomplished based on one-dimensional NUFFT.

Various embodiments of the present disclosure have been described above, and the foregoing descriptions are exemplary, not exhaustive, and not limiting of the disclosed embodiments. Numerous modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims (7)

1. A method of three-dimensional imaging based on an array of reconfigurable electromagnetic surfaces, the method comprising:

the reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area, and comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, wherein the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer;

aiming at that a multichannel transmitting digital beam of each reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of a reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam are orthogonal in space and synthesized into a multichannel digital synthesis beam of a transmitting and receiving subarray, and focusing the multichannel digital synthesis beam to a corresponding position of a three-dimensional imaging target area is a transmitting and receiving subarray scanning beam;

performing phase compensation on overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams;

and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area.

2. The three-dimensional imaging method according to claim 1, wherein the reconfigurable electromagnetic surface emitting subarray comprises a transmission feed, a diode phase control array and an antenna element;

the reconfigurable electromagnetic surface receiving subarray comprises a receiving feed source, a diode phase control array and an antenna unit.

3. The three-dimensional imaging method of claim 2, wherein said adjusting phases of the multi-channel transmit digital beams of the reconfigurable electromagnetic surface transmit sub-array and the multi-channel receive digital beams of the reconfigurable electromagnetic surface receive sub-array comprises:

and adjusting the on-off state of the diode phase control array of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phases of the antenna units of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, and adjusting the phase of the multichannel transmitting digital beam and the phase of the multichannel receiving digital beam according to the phases of the antenna unit array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray to form a transmitting-receiving subarray scanning beam.

4. The three-dimensional imaging method according to claim 2, wherein the digital beamforming of the multi-channel transmission signals according to the adjustment of the phase of the transmission feed signal and the digital beamforming of the multi-channel transmission signals according to the adjustment of the phase of the transmission feed are spatially orthogonal as a multi-channel digital synthesized beam of the transmit-receive subarray.

5. The three-dimensional imaging method according to claim 1, wherein the phase compensation of the overlapping array elements of the reconfigurable electromagnetic surface transmit sub-array and the reconfigurable electromagnetic surface receive sub-array comprises:

and according to the phase distribution of the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, carrying out phase compensation on the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray by using a phase matching adjustment method of an average phase.

6. Three-dimensional imaging method according to claim 1,

and obtaining a multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray by using a non-uniform fast Fourier transform algorithm, wherein the multichannel transmitting digital beam and the multichannel receiving digital beam are orthogonal in space to form a multichannel digital synthesis beam of the transmitting subarray.

7. A method of three-dimensional imaging according to claim 1 wherein the total array of reconfigurable electro-magnetic surfaces is cross-shaped, T-shaped, r-shaped.

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